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d ' r: <br /> Supplemen al Investigation Work Plan <br /> BP Oil Site No. 11193 <br /> C A M B R I A Stockton, California <br /> February 25, 2000 <br /> Site Hydrogeology: The soils encountered beneath the site consist of several feet of fill and up to r <br /> 5 feet of clay which are underlain by silt and sand mixtures to the total depth explored of 30 feet bgs. <br /> CPT electric logs were more detailed but generally consistent with adjacent boring logs based on <br /> soil samples collected at 5-foot intervals. For example, the CPT electric logs indicate the presence <br /> of several clay or silt intervals that were not described in adjacent borings. <br /> Soils encountered in the previously mentioned Caltrans well consisted of interbedded sands and <br /> clays to approximately 180 feet bgs, which was underlain by a 20-foot thick sandstone unit, then <br /> interbedded sands and clays to approximately 347 feet bgs, and a siltstone to a total explored depth <br /> of 350 feet bgs. A clay unit was noted between 43 and 80 feet bgs (see Appendix B). <br /> Water levels In site monitoring wells have risen 8 to 10 feet since 1992. In October 1999, <br /> groundwater was encountered at 11 to 14 feet bgs and the groundwater flow direction ranged from <br /> northeasterly to southwesterly. This broad range of groundwater flow directions has been shown <br /> using wells screening similar intervals and soil types during previous groundwater monitoring <br /> events. Rose diagrams constructed using one average groundwater flow direction for each <br /> monitoring event would oversimplify site conditions and may not be representative of the aggregate <br /> groundwater flow direction at the site. <br /> Slug tests performed on wells MW-1, MW-.2 and MW-5 indicate that the hydraulic conductivity <br /> ranges from 8.68 x 10-5 to 4.48 x 10-4 <br /> centimeters per second (cm/sec) with an average of <br /> 2.53 x 10-4 cm/sec (see Appendix A). Based on this average value, a typical hydraulic gradient of <br /> 0.007, an effective porosity of 0.3, and using the appropriate unit conversions, a groundwater flow <br /> velocity of 6.0 feet per year is calculated using the relationship shown below. <br /> i <br /> v=kiln <br /> 1 <br /> where: v=groundwater flow velocity (feet per year) <br /> k=hydraulic conductivity (cm/see) <br /> h i =hydraulic gradient (feet/feet) <br /> r n=effective porosity (unitless) l <br /> using the conversion factors: <br /> 1 foot= 30.48 cm <br /> 1 year=365 days/yr * 24 hrs/day * 60 min/hr * 60 sec/min <br /> s <br /> 5 <br />